This thesis provides an analysis of some recent reforms to corporate and personal income taxes. The first reform considered is the UK reform of dividend taxation in 1997. This abolished the repayability of tax credits to pension funds and thus reduced the value of dividends to one group of shareholders. Using the tax-adjusted CAPM (Brennan, 1970) we show that such a reform is unlikely to affect share prices strongly. We then provide empirical evidence for this and explain why previous research (Bell and Jenkinson, 2002) came to a different conclusion. We also consider the effects on dividend payments and company investment. Then we turn to the introduction of a flat-rate income tax in Russia, which dramatically reduced tax rates for better-off individuals. This was accompanied by a strong increase in revenues and we investigate whether this was caused by the reforms. A brief summary of the theoretical predictions concerning labour supply and compliance suggests that this is unlikely. Using micro-data on individuals and households, and employing a difference-in-differences method, we confirm that the reform does not appear to have caused the revenue boom, although we find some evidence of improvements in compliance. Finally we consider international corporate income tax reforms. We start with an analysis of the properties of alternative tax measures including a newly proposed one using UK data. We find that different approaches can give rise to very different quantitative estimates of tax rates, and even different estimates of measures based on the same approach can diverge strongly. We then apply the discussed measures in an analysis of corporate income tax reforms in OECD countries. We develop a number of stylised facts and discuss possible interpretations, based both on existing models and a new explanation. We also relate these findings to recent international initiatives in tax co-operation.